Xpath 匹配節點的內容為空白（inner text 為空白）

需求是從以下寫出能從下面的xml中取出Title內容（inner text）為空白的節點的XPath： 

<?xml version="1.0" encoding="utf-8" ?><BookCatalog><Books><Book><Title>Asp.net</Title><Price>22.5</Price><Author>Abraham</Author></Book><Book><Title></Title><Price>22.5</Price><Author>Abraham</Author></Book></Books></BookCatalog>

容易寫出錯誤的xPath有:

//Book[Title[text()='']] //Book[Title[text() is null]] //Book[Title[node() is null]] //Book[Title[. is null]] //Book[Title[text()=]] 

正確的寫法為：

//Book[Title[not(text())]] 或  //Book[Title[not(node())]]

驗證程式為：

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Xml;namespace TestXPath{    class Program    {        static void Main(string[] args)        {            string[] errorXPaths = { "//Book[Title[text()='']]",                 "//Book[Title[text() is null]]",                 "//Book[Title[node() is null]]",                 "//Book[Title[. is null]]",                "//Book[Title[text()=]]"};            string[] correctXPaths = { "//Book[Title[not(text())]]", "//Book[Title[not(node())]]" };            string xml = "<?xml version=\"1.0\" encoding=\"utf-8\" ?> " + @"                        <BookCatalog>                        <Books>                        <Book>                        <Title>Asp.net</Title>                        <Price>22.5</Price>                        <Author>Abraham</Author>                        </Book>                        <Book>                        <Title></Title>                        <Price>22.5</Price>                        <Author>Abraham</Author>                        </Book>                        </Books>                        </BookCatalog>";            XmlDocument xmlDocument = new XmlDocument();            xmlDocument.LoadXml(xml);            foreach (string errorxPath in errorXPaths)            {                try                {                    XmlNodeList nodeList = xmlDocument.SelectNodes(errorxPath);                    Console.WriteLine("errorxPath:" + errorxPath);                    Console.WriteLine("nodeList.Count:" + nodeList.Count);                }                catch (Exception ex)                {                    Console.WriteLine(ex.Message);                }             }            foreach (string correctXPath in correctXPaths)            {                XmlNodeList nodeList = xmlDocument.SelectNodes(correctXPath);                Console.WriteLine("correctXPath:" + correctXPath);                Console.WriteLine("nodeList.Count:" + nodeList.Count);            }            Console.Read();        }    }}